1. Field of the Invention
This invention relates to a catadioptric lens barrel which can be attached to an optical projection unit, such as a projection exposure apparatus used to manufacture semiconductor wafers. More particularly, the present invention relates to a catadioptric lens barrel structure including its support structure. The lens barrel structure comprises a plurality of lens barrels aligned in parallel, and each lens barrel comprises a plurality of sub-barrels.
2. Description of the Related Art
A lens barrel is a tubular mechanical structure containing a series of lenses which are aligned to transfer an image from one end of the lens barrel to the other. The lens barrel may include a sturdy threaded body and durable metal retaining rings, often referred to as a sub-barrel, to carry a series of lens holders, commonly referred to as cells. Another type of lens barrel is known as a catadioptric lens barrel. A catadioptric lens barrel contains not only refractive elements, such as lenses, but also reflective elements, such as mirrors.
Both of these lens barrel designs are used in conventional optical systems. For example, an optical projection unit often has a lens barrel and may be used in a projection exposure apparatus for production of semiconductor wafers. The projection exposure apparatus includes a reticle positioned near an entrance end of the lens barrel and a semiconductor wafer positioned near an exit end. The projection exposure apparatus shines light through the reticle, optically reduces a pattern on the reticle, and transfers the pattern through the lens barrel onto a predetermined area on the semiconductor wafer. The semiconductor wafer is a silicon wafer with a photo-sensitive coating or layer for making semiconductor devices, such as microprocessor or memory chips.
A catadioptric lens barrel system using two or more parallel lens barrels offers benefits not found in conventional single barrel systems. Placing the lens barrels in parallel reduces the overall height of the lens barrel system, but increases the overall width. Reduced height is important for many reasons, such as for ease of transport. This type of catadioptric lens barrel design, however, poses several problems. First, keeping proper alignment of a plurality of parallel lens barrels can be difficult. Second, the focus depth of the projection system changes as temperature changes. Coefficients of thermal expansion of the lens barrels and their internal components, and the indices of refraction of the lens materials vary with temperature. Errors related to these factors collectively alter the focusing properties of the optical system. Third, the parallel lens barrel structure tends to be more sensitive to movement or vibration than conventional single barrel designs.
In light of the foregoing, there is a need for a catadioptric lens barrel structure that holds the lens barrels stabily and accurately, and minimizes distortion errors due to temperature changes, vibrational, or other external forces, so that the reticle pattern remains focused as it is transferred and reduced to the wafer.
Apparatus and methods consistent with the principles of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, one aspect of the invention is directed to a stable lens barrel structure that minimizes the effects of environmental changes. The lens barrel structure may be used, for example, in a projection exposure apparatus in semiconductor manufacturing to reduce a pattern on a reticle through the projection exposure apparatus to a semiconductor wafer.
The lens barrel structure comprises a lens barrel and a support structure. The lens barrel comprises a plurality of sub-barrels serially aligned along an optical axis of the lens barrel. Each sub-barrel has an optical sub-axis. The plurality of optical sub-axes substantially coincide with the optical axis. The support structure supports each sub-barrel and maintains the alignment of the corresponding optical sub-axes to the optical axis. A second aspect of the invention is directed to a lithography system comprising a lens barrel structure consistent with such a lens barrel system.
A third aspect of the invention is directed to a lens barrel structure comprising a plurality of lens barrels and a support structure. Each lens barrel comprises a plurality of sub-barrels aligned along an optical axis of the lens barrel. The optical axes of the lens barrels are substantially parallel to each other while the optical sub-axes are serially aligned along the corresponding optical axis of each lens barrel. The support structure supports each sub-barrel and maintains the substantial parallel alignment of the optical axes. A fourth aspect of the invention is directed to a lithography system comprising a lens barrel structure consistent with such a lens barrel system.
A fifth aspect of the invention is directed to a method for aligning a plurality of sub-barrels serially aligned along an optical axis. Each sub-barrel has an optical sub-axis. The plurality of optical sub-axes substantially coincide with the optical axis of the lens barrel. The method comprises the steps of supporting each sub-barrel and maintaining the alignment of each optical sub-axis to the optical axis using a plurality of adjustment articles.
A sixth aspect of the invention is directed to a method for making a lens barrel structure. The method comprises the step of providing at least one lens barrel. Each lens barrel comprises an optical axis and a plurality of sub-barrels. Each sub-barrel has an optical sub-axis. The optical axes of the lens barrels are substantially parallel to each other. The sub-barrels are serially aligned along the corresponding optical axis of the lens barrel. The method also comprises the step of supporting each lens barrel to maintain the substantially parallel alignment of the optical axes, and the step of removably fastening each sub-barrel to a support structure.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The advantages and purposes may be obtained by means of the combinations set forth in the attached claims.